When you place an order it has to go through several processes before the order completes. First your bank has to check that your account has enough money and if so it will set aside the amount needed and mark it as 'pending' until all the processes are complete.
Important to note, the money doesn't actually leave your account even though it looks like it has, it's just reserved by your bank.
Next it goes to the payment system, (in our case if you haven't chosen PayPal it is Shopify Pay) which then checks various things such as address, CVC code, country, IP address etc. If this passes then the order is sent to us and we receive the money and you get a confirmation email with an order reference and we'll process it as normal.
If however this fails for whatever reason, the transaction goes no further and we don't receive the order or the money and you won't get any email confirmation from us.
Your bank will then revert the 'pending' funds back to being available but it can take several working days depending on your bank.
This is why sometimes it looks like you've paid for something when no order has completed. Frustrating and annoying but standard practice from the banks to help protect you and unfortunately something that is out of our hands.
We always recommend simply placing the order again and often it's an issue with the address you entered for billing so just be careful when entering it.
If at any point you're unsure or would like any reassurance, please contact us and to be sure, you're also most welcome to contact your bank directly to double check as well.